1. Field of the Invention
The present invention relates to jet aviation noise, and particularly to a passive edge-tone suppression method.
2. Description of the Related Art
In modern aviation industry, every day many commercial aircrafts take-off and land at different countries across the globe, producing undesirable noise pollution to the nearby communities. The noises produced by aircraft components, such as the wings, slats, flaps, and landing gear, among others, are some of the vital sources of sound. Even in fighter/bomber weapons bays, at moderately high speeds, open cavities can produce undesirable noises. This can lead to the structural fatigue of internally carried weapons, their suspension equipment, and the structural loads on the parent aircraft.
Researchers have included the oscillations from the flutter of aircraft wings in the class of self-sustained oscillations, since the vibration results through partial conversion of energy from a steady flow into oscillations. Self-sustained shear oscillations are found in various shear layer impingement configurations, which are responsible for the flow-induced noise and vibration. This can result in unwanted structural loading, and appears in a range of applications, such as transonic wind tunnels, aircraft components, slotted flumes, high-head gates, velocity probes, and pressure probes, among other applications. Flow-induced noise sources are one of the relatively complicated flows, which can be challenging to simulate.
Edge-tone, a typical phenomenon of these self-sustained shear oscillations, is generated when a jet of air impinges on an edge or the sharp edge corner of a wedge. When the free shear layer near the nozzle lip is excited, a disturbance is initiated and convected downstream and amplified. Further, if the disturbance is unstable, it forms into organized vortices. When these vortices impinge on the edge, pressure waves are generated and propagate upstream to the nozzle lip, producing another disturbance near the nozzle lip. This upstream propagating sound and the convected downstream disturbances constitute a feedback loop.
Since the edge-tone is a loud noise with high amplitude, it could lead to structural damage. Therefore, attempts to suppress edge-tone have been undertaken. Although these attempts have met with some success, there is still a need for a technique that reduces the jet noise effectively.
Thus, a passive edge-tone suppression method solving the aforementioned problems is desired.